The invention relates generally to voltage regulator circuits and, more particularly, to voltage regulator circuits that are required to provide a widely varying load current.
Many electrical devices have multiple modes of operation that each draw a different level of current from an associated power supply. These multiple modes of operation will often be used, for example, to facilitate power conservation within the device. For example, a handheld communicator unit that utilizes a battery as a power source will typically switch between a number of different modes during operation of the communicator to minimize the current draw from the battery. In one scenario, for example, a communicator will switch between a low current sleep mode, a medium current communicate mode, and a relatively high current operate mode when the communicator is turned on. Many other scenarios are also possible.
In the past, a single voltage regulator was commonly used to generate a regulated supply voltage for all of the different operating modes of an electrical device. Naturally, the maximum current of the voltage regulator had to be adequate to handle the highest possible current to be drawn by the device. To maintain stability within a voltage regulator, the quiescent current of the regulator is typically between 0.1 and 3 percent of the maximum current of the regulator. This quiescent current flows regardless of the present output current of the regulator or the present mode of operation of the driven device. Thus, a relatively large quiescent current will flow in the regulator even when the driven device is in a very low current sleep mode. As can be appreciated, this relatively large quiescent current can represent a significant power drain in an electrical circuit. This power drain is especially troublesome in circuits having limited available power, such as battery driven circuits.